1. Kirov A S, MSKCC Overview of Geant4 Use and Issues in Imaging: Emission Tomography (PET and SPECT) Assen S. Kirov Department of Medical Physics Memorial Sloan-Kettering Cancer Center New York

2. Kirov A S, MSKCC Why simulate imaging systems and scans ? Better understand and model phenomena affecting image quality and accuracy Optimize scan imaging and processing parameters Calculate parameters needed for improved image reconstruction

3. Kirov A S, MSKCC Basis of this talk Membership in the OpenGATE collaboration ( www.opengatecollaboration.org )www.opengatecollaboration.org Whose goal is -the creation of an elaborate and flexible Monte Carlo program that allows realistic simulation of the physical processes, detector geometry and all factors affecting emission tomography applications -realistic modeling of patient and small animal anatomy - based on GEANT4

4. Kirov A S, MSKCC Basis of this talk Product of OpenGATE : GATE (GEANT4 Application for Tomographic Emission) Widely used for – PET – SPECT Potential for CT (why not ?) Potential for Radioimmunotherapy and Nuclide Therapy dosimetry Jan et al, PMB 49 (2004) 4543

5. Kirov A S, MSKCC Use of GEANT4 prior to GATE for imaging GEANT3 and GEANT4 based codes –example Jan S (Thesis) : GePETos Summary of other codes: –Buvat and Castiglioni (Q J Nuc Med, 46, p 48-61, 2002)

6. Kirov A S, MSKCC GATE architecture GEANT 4 Core Layer Application Layer User Layer Jan et al, PMB 49 (2004) 4543

7. Kirov A S, MSKCC User Layer … /gate/block/daughters/name crystal /gate/block/daughters/insert box /gate/crystal/placement/setTranslation 0.0 0.0 0.0 mm /gate/crystal/geometry/setXLength 30.0 mm /gate/crystal/geometry/setYLength 4.4 mm /gate/crystal/geometry/setZLength 4.75 mm /gate/crystal/setMaterial BGO … -Verbosity and visualization -Geometry -Digitizer -Physics -Sources -Outputs -Experiment

8. Kirov A S, MSKCC GATE systems Geometry organization: Hierarchical structures –For realistic signal processing organization –Simplifies geometry input GATE system: {Hierarchically organized geometry + corresponding LMF output} 5 GATE systems SPECT - 1 PET – 3 (2 block based, 1 pixelated) Generic -1 Jan et al, PMB 49 (2004) 4543

9. Kirov A S, MSKCC GATE time and movements Needed for: - Patient and organ motion - Scanner rotation - Activity distribution changes GEANT4 limitations: - geometry: static during simulation - no source movements Solutions in GATE: - Geometry updated between simulation time steps - The source is confined to a smaller volume moving inside a larger emission volume Santin et al, 2003 Strul et al, 2003 Jan et al, PMB 49 (2004) 4543

10. Kirov A S, MSKCC GATE physics Sources –Particle type, position (volume), direction (solid angle), energy (spectrum), activity –Modified GEANT4’s RDM – virtual clock defines absolute time used to initialize GEANT4’s internal tracking time –Multiple, voxelized sources –e + emission (Jan 2002): »  + spectra parametrization - faster »annihilation photon noncolinearity GEANT4’s interaction processes and cuts Jan et al, PMB 49 (2004) 4543

11. Kirov A S, MSKCC GATE digitization - Resolution blurring, spatial blurring, crosstalk - Parallelizable and non-parallelizable dead times - Coincidence processing - Post simulation processing of output files stored before digitization

12. Kirov A S, MSKCC GATE validation PETat least 5 patient and microPET scanners energy spectra, sensitivity, resolution, scatter faction, count rates, image quality, contrast recovery SPECT at least 5 systems energy spectra, sensitivity, resolution,… Prototypeat least 4 systems energy spectra, sensitivity, resolution… More than 15 references in Jan et al, PMB 49 (2004) 4543 and at www.opengatecollaboration.org

13. Kirov A S, MSKCC GE Advance/ DLS PET scanner

14. Kirov A S, MSKCC MC based coincidence count rates for IQ phantom See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this meeting NECR Scattered Trues Randoms

15. Kirov A S, MSKCC Other issues CT simulations – GATE could handle the geometry, not tested yet Optical imaging – very promising field for GEANT4 : small animal; 3D dosimetry (see Kirov et al, SU-FF-T-229 at this meeting), etc. Worst GATE/GEANT4 problem for imaging »Very time consuming simulations 35 CPU days on 2 GHz !!

16. Kirov A S, MSKCC Conclusions GEANT4 with GATE- powerful, flexible, convenient for use and accurate tool for nuclear medicine imaging applications GEANT4 without GATE: worth pursuing only if a new approach can drastically improve performance Efficiency: work needed